1. Field of the Invention
The present invention relates to a capacity control valve, and more particularly to a capacity control valve for controlling discharge capacity of a variable capacity compressor provided to a vehicle air conditioner.
2. Description of the Related Art
The variable capacity compressor disclosed for example in Unexamined Japanese Patent Publication No. 11-218078 is provided with a capacity control valve. The capacity control valve comprises a valve member and an electromagnetic drive unit for driving the valve member. The valve member is driven by the electromagnetic drive unit to open/close a valve passage, and the valve passage links the discharge chamber of the compressor to the crank chamber thereof.
The electromagnetic drive unit includes a movable iron core or plunger coupled to the valve member. The plunger is inserted into a cylinder bore defined in the electromagnetic drive unit.
More specifically, the plunger has one end on the valve member side, which partitions the cylinder bore into an inlet chamber, and a refrigerant is made flow from a suction chamber of the compressor into the inlet chamber. The inlet chamber is connected to a pressure-sensitive chamber disposed on the other end side of the plunger, and a bellows is located in the pressure-sensitive chamber. The bellows is expanded/contracted by pressure of the suction chamber and mechanically connected to the valve member via the plunger. Therefore, the bellows applies a urging force corresponding to the pressure of the suction chamber to the valve member.
When the solenoid of the electromagnetic drive unit is excited, the valve member is driven by the solenoid in the closing direction thereof. Thus, the opening of the valve member, namely the pressure of the crank chamber, is adjusted by the driving force of the solenoid and the urging force of the bellows.
Since the plunger forms the inlet chamber as mentioned, the one end face of the plunger receives the pressure of the suction chamber and is exposed to the refrigerant. As a result, the atomized lubricating oil that is mixed into the refrigerant is liquefied in the inlet chamber, and the liquefied lubricating oil intrudes into a gap between the plunger and the inner peripheral surface of the cylinder bore.
The gap is extremely narrow, so that the lubricating oil that has intruded into the gap increases the sliding resistance of the plunger due to its viscosity. In the worst case, the gap is blocked up with the lubricating oil, which causes the chamber located on the other end side of the plunger to be sealed in an airtight manner. In this case, even though the electromagnetic force of the solenoid is changed in some measure, the plunger remains being jammed, thereby hindering the smooth opening/closing operation of the valve member. This destabilizes pressure adjustment in the crank chamber, that is, the discharge capacity control of the compressor.